This invention relates to a multiple control valve system of a hydraulic circuit for operating a working machine.
There are many working machines each including a number of elements respectively actuated by piston-cylinder assemblies actuated by pressurized oil. For the sake of brevity, such piston-cylinder assembly is hereinafter merely called an actuator. In a working machine including a large number of actuators, some of them are operated by pressurized oil supplied by one oil pump, while the other actuators are operated by the pressurized oil supplied by another oil pump.
A hydraulic power shovel of a civil machine, which is one typical example of a large working machine, is controlled by first and second multiple control valves operatively connected to hydraulic pumps, in which the first multiple control valve controls actuators for a running (right or left), swivelling and arm mechanisms of the machine by the operation of three direction change-over valves disposed therein and the second multiple control valve controls actuators for a running (left or right) mechanism, a boom and a bucket of the power shovel. The first and second multiple control valves each including three direction change-over valves are attached to a mount disposed at a limited place in the power shovel.
In one specific use of the multiple control valve system of the type described above to increase operating flow amount of pressurized oil in a bucket of a power shovel, a multiple control valve including four-series direction change-over valve means is used as a first multiple control valve instead of the first multiple control valve having three-series direction change-over valve described above without changing the second multiple control valve in a manner that one of the four-series direction change-over valves is connected to a bucket actuating circuit of the second multiple control valve to join flows of pressurized oil which passes through the first and second multiple control valves. However, it is considerably difficult to set or attach a multiple control valve including four direction change-over valves to a mount attached at a limited place of the power shovel instead of an existing multiple control valve including three direction change-over valves. Moreover, even if these multiple control valves could be exchanged by newly adding a mount member, much time and many steps are required for attaching or detaching these heavy multiple control valves and conduits or other members which are to be connected to the multiple control valve exchanged.